CHEMICALLY-INITIATED ELECTRON-EXCHANGE LUMINESCENCE OF SILYLOXYARYL-SUBSTITUTED SPIROADAMANTYL DIOXETANES - KINETICS AND EXCITED-STATE YIELDS

The kinetics of the fluoride-induced decomposition of the thermally st able silyloxyaryl-substituted spiroadamantyl dioxetanes 1a,b and the e xcited state formation of this chemically initiated electron exchange luminescence (CIEEL) have been investigated, Two limiting kinetic regi mes flash and glow have been identified, which depend on the fluoride concentration, the first at high, the second at low [F-] triggering, w hose detailed kinetic analysis affords the rate constants for the depr otected dioxetanes 2a,b cleavage in acetonitrile and dimethyl sulfoxid e and chemiluminescence measurements the CIEEL and phenolate 4 (CIEEL emitter) excitation yields, Chloro-substitution in the spiroadamantyl dioxetane does not affect the deprotection step k(2) but leads to a ca five-fold faster cleavage of the deprotected dioxetane 2, while the c hemiexcitation yield is the same for both dioxetanes, The energies of the first excited singlet and triplet states of the emitting phenolate 4 were estimated by AM1 configuration interaction calculations with e xplicit consideration of acetonitrile as solvent (self-consistent reac tion field approach), The first excited singlet and triplet state of t he CIEEL emitter phenolate 4 possess pi, pi character, as suggested b y the pi-type molecular orbitals and the large singlet-triplet energy gap, The chemiexcitation of both singlet and triplet states of the exc ited phenolate 4 is feasible during the dioxetanes 1a,b cleavage, but the experimentally determined high singlet excitation yields suggest t hat preferentially the phenolate 4 singlet state is populated in the f luoride ion-triggered CIEEL process.